1. Field of the Invention
The present invention relates to a power-saving circuitry and method of CPU, and more particularly, to a power-saving circuitry and method of CPU in which the operating voltage is adjusted by changing the voltage identification code.
2. Description of the Related Art
The operating voltage of the CPU in the computer system is determined by a voltage identification code (VID) generated based on its operation mode.
FIG. 1 schematically shows a block diagram of a circuit for providing an operating voltage to the CPU in the prior art. Referring to FIG. 1, the voltage identification code VID is generated in a common computer system based on the required operating voltage Vcore. As shown in FIG. 1, the CPU 101 outputs the voltage identification code VID to a pulse width modulator (PWM) device 103. The pulse width modulator 103 determines a magnitude of the operating voltage Vcore providing to the CPU 101 based on the voltage identification code VID.
The magnitude of the operating voltage required by the CPU is not consistent. For example, when entering a power-saving mode (such as a C3 state), the operating voltage required by the CPU is lower than that required under normal operation. However, some CPU (such as Celeron Pentium M series CPU) do not automatically lower the operating voltage after entering the power-saving mode, thus the power-saving efficiency is rather poor in computer systems with this type of CPU. If laptop computers use such type of CPU with low power-saving efficiency, the life span of the battery would be shortened accordingly.
As aforementioned, such type of CPU with low power-saving efficiency is not the mainstream product in the market. However, in order to reduce the manufacturing cost of the computer system, these CPUs with low power-saving efficiency are still used in some cases. Therefore, how to enhance the power-saving efficiency for the computer system with this type of CPU has become imperative.